1. Field of the Invention
This invention relates to a novel process for producing low molecular weight styrene polymers or low molecular weight copolymers of styrene and another vinyl type monomer.
2. Description of the Prior Art
Heretofore, there have been proposed mainly the following methods for producing low molecular weight styrene polymer having a number average molecular weight of less then 5000.
(1) Radical telomerization PA1 (2) Ion telomerization PA1 (3) Thermal polymerization
The method (1) and the method (2) carry out the polymerization in the presence of a large quantity of chain transfer agents such as halogen compounds, mercaptan compounds and the like and the method (3) is a solution polymerization method in which the polymerization is carried out in the presence of a large quantity of solvent which easily undergoes chain transfer, such as cumene, benzyl alcohol derivatives and the like.
The method (1) and method (2) introduce fragments of the chain transfer agents, namely halogen, mercaptan and the like, into the end parts of the obtained polymer chain with the result being that the thermal stability thereof is decreased and they are possibly decomposed which is not preferred because of environmental pollution.
Both methods require recovery of the solvent because a large quantity of the solvent is used and they also require the use of a sealed apparatus because many chain transfer agents used in the methods generally have bad odours and are poisonous and, further, a process for separating the chain transfer agents from the resultant product is required. Accordingly, both methods have disadvantages in that complicated procedures are needed.
Further, the method (2) has troubles in that according to the method (2), it is difficult to eliminate the catalysts remaining in the obtained polymers and the catalysts used in the method (2) are in general unstable in water.
Because the method (3) also looses much energy during the procedures and a large and strong polymerization apparatus is required, it is unpreferable for producing low molecular weight styrene polymers.
Another method involving increasing the quantity of the polymerization initiator has been contemplated.
However, it is difficult by that method to obtain polymers having a definite value of number average molecular weight, because the polymerization temperature therefor is difficult to control. Further it was found that even if the quantity of the polymerization initiator was increased, the effect on lowering the number average molecular weight of the polymers was small. (refer to Japanese Patent Publication No. SH049--2340)
Concerning polystyrenes in general, they are defined as polymers having number average molecular weights in the order of several millions and they are used mainly as molding materials. Low molecular weight polystyrenes generally have number average molecular weight of from several hundreds to several tens of thousands and they are used in many fields.
The low molecular weight styrene series polymers are useful, for example, as base materials for toners of electrophotography and for hot melt type coating materials, pigment dispersants, and tackifiers.
Also the low molecular weight styrene series polymers possess high reactivities so that they can be transformed into many kinds of derivatives. For example they are used for synthesizing a low molecular weight polystyrenic acid by sulfonation of the phenyl groups thereof and also they are used for introducing quaternary ammonium groups into the phenyl groups by chloromethylation and quaternary ammoniazation.
Further they are useful as intermediates.